A pneumatically operated ram boring machine having a striking tip held in a cylindrical housing and a striking piston reciprocating in the housing is known from German patent specification No. 21 57 259. The automatic piston of this machine applies periodic ramming blows to the movable striking tip. The striking tip is supported on the housing through a compression spring and moves into the ground in an oscillating manner under the influence of these ramming blows and finally pulls the housing after it when its stroke is complete.
On the other hand a ram boring machine is known from German Offenlegungsschrift No. 21 05 229 in which the striking tip is a fixed component of the machine housing.
Ram boring machines of this kind are a preferred means of laying service lines such as those for water supply and drainage, for electric power or for telephone connections underground without the need to dig trenches. The ram boring machine moves in the ground, forcing aside and compacting the earth as it drives forwards and forming a tunnel into which a service line or cable can be inserted without difficulty.
The design of the ram boring machines according to the prior art is such that only substantially straight bores or earth tunnels can be made, i.e. the working direction cannot be changed once it has been set. Machines of this kind are also described for example in German patent specifications Nos. 23 40 751 and 26 34 066.
However, in practice it has been found that uncontrollable directional deviations can occur, especially in non-homogenous ground and in particular when covering long distances. As a result there is an urgent technical need for a ram boring machine whose working direction can be controlled and steered. Steerability is also necessary, for example, to enable the machine to avoid particularly large obstacles or other service lines crossing its path.
A self-propelled ram boring machine, in particular for making earth bores, having an impact head acted on by a striking piston reciprocating in the machine housing and having guiding surfaces for controlling the course of the machine is known from German patent specification No. 30 27 990. A characteristic of this machine is that the striking tip has an oblique front face. Interchangeable oblique front faces having different oblique angles may, for example, be provided. The oblique face can also be roof-shaped.
The advantage of this kind of machine is that the oblique face gives the ram boring machine a component of movement in the ground perpendicular to its axis, which results in the earth bore made by the ram boring machine following a curved course. The radius of the curve depends on the oblique angle of the oblique face, so that different radii can advantageously be obtained by the use of interchangeable striking tips with oblique faces having different oblique angles. Another possibility is to use an adjustable oblique face on the striking tip. The alternative roof shape increases the driving capacity of the machine.
Even with this known machine the predetermined curved course cannot be changed or influenced as desired during uninterrupted forward movement and thus the machine cannot be deliberately steered.